On 08/05/2018 05:38 AM, Chris Hamilton ultrabat@gmail.com [harryproa] wrote:

 

Thanks for the response Rob.  Assuming lighter high quality ply epoxied would be more expensive but very little glass is required and foam is pricey, so would there be that much difference???  

Is the Pacific Marine product (Australian) toxic? - I am using it and I think not, and is very simple to apply with a roller, and no mess that you could complain about.  I am borrowing someone's Festool sanding etc. equipment with dust extractor, and there is absolutely no dust whatsoever.

Anyway, with all the discussion about foams over the last few months, the point I was raising is that it seems that there is still some uncertainty in that direction, whereas marine ply, properly maintained, is totally proven.  But if it would kill off the speed of the boat, one would be best to avoid it..

What thickness ply would be recommended for your designs?

Chris Hamilton

     I've been looking into Richard Woods Sagitta more, including the option of building the hulls above the knuckle using sandwich.   Interestingly the GSM Rob calls for foam to replace plywood is very little more than what Richard calls for on plywood....Note that he calls for biax instead of cloth on the outside.     I've learned that he offers the option of 1/2" foam, no stringers, but don't know what he calls out for glass with the foam.  My guess would be very little more.  I'm hoping to wheedle that info out of one of the builders.

    Richard has offered to supply me with the hull drawings for the Eclipse hulls if I buy the Sagitta plans, as well as some support in marrying the two designs.   The reason is my payload concerns.   At 2' longer, and a ton more displacement, Eclipse has only 120 lbs more payload.  Most of the weight difference is in the larger bridge deck cabin and 6" more freeboard, both of which I would be eliminating if marrying the two designs.   The result would be 2' more boat than I want, but at least 1500 pounds more payload......even more if built in foam sandwich.   This pretty much nails it for me.   I don't need or want the larger cabin of Eclipse.... while space is nice, payload is far more important to me.  It will also yield a larger cockpit.  

    Below are some numbers from Woods Design and and from an Email Rob wrote awhile back:

                                                                                                H.W.

 

Below is the glass called out on the Woods Eclipse hulls for 9mm ply above the knuckle:

Glass - (ply topsides) 600g biaxial 70Kgs plus 300g cloth 10Kgs, Epoxy glue
200Kgs

Below is Richard's equivalancy in foam sandwich for 9mm ply:

If we leave the stringers in and size the foam/glass for the same stiffness as the ply, we have
30 sq m of 6mm foam with 200 glass each side 30 x (0.5+.2+.2+.2+.4) = 45 kgs
and 156 sq m of 10mm foam with 600 gsm glass outside and 400 inside =156 x (.8+.4+.6+.5+.4)= 421 kgs.
The numbers in brackets are the weights per sq m of the foam+ inside glass+outside glass+infused resin at 1:2 resin fibre+resin to wet the foam both sides.
Total = 466 kgs